Electric cables



y 1965v J. M. RICHARDS 3,193,614

ELECTRIC CABLES Filed Aug. 3, 1962 3 Sheets-Sheet 1 y 1965 J. M.RICHARDS 3,193,614

ELECTRIC CABLES Filed Aug. 3, 1962 v 3 Sheets-Sheet 2 /24- ::I. I i 25-a 3P FIG. 11. 4f

y 1965 J. M. RICHARDS 3,193,614

ELECTRIC CABLES Filed Aug. 3, 1962 3 Sheets-Sheet 5 United States PatentM 3,193,614 ELECTRIC CABLES Joseph M. Richards, Scdgley, England,assignor to The Wednesbury Tube Company Limited, Bilston, England, aBritish company Filed Aug. 3, 1952, Ser. No. 214,599 Claims priority,application Great Britain, Aug. 5, 1961, 28,521/61 8 Claims. (61.174-412) This invention relates to electrical cables of the kindcomprising a tubular metal sheath and two or more conductor coresextending through the sheath and separated from each other and from thesheath by a filling of powdered insulating material. Such cables arehereinafter referred to as being of the kind specified.

Cables of the kind specified are usually made by disposing the requisitenumber of conductor-cores within a tubular sheath to extendlongitudinally thereof in at least approximately the positions whichthey are required to occupy in the finished cable, the sheath and theconductor cores being of cross-sectional dimensions larger than thosewhich they are required finally to have, filling the space between theconductor cores and between the conductor cores and the sheath withpowdered insulating material and compacting the latter, for example, byramming the powdered material in the sheath in an endwise direction, andsubjecting the filled sheath with the conductor cores therein to adrawing operation to reduce the cross-sectional dimensions of thesheath, conductor cores, and filling of insulating material. This methodof manufacture is hereinafter referred to as being of the kindspecified.

One of the requirements which arises in cables of the kind specified isto be able to identify an exposed conductor core at one end of the cableand an exposed conductor core at the other end of the cable as beingparts of the same conductor core.

The object of the present invention is to provide a new or improvedmeans for meeting this requirement.

From one aspect the present invention resides in the provision of acable of the kind specified wherein one at least of the conductor coreshas a longitudinally extending recessed formation in its surface.Preferably the recessed formation is filled with a material whichpresents a contrasting visual appearance in comparison with thatpresented by the surface of the conductor core itself.

Advantageously, but not essentially, the material with which the recessor each of same is filled may be the powdered insulating materialincorporated in the cable;

The preferred form of recessed formation is a continuous groove whichextends longitudinally of the conductor core concerned. 7

Ordinarily it is suificient for one only of the conductor cores toincorporate the recessed formation. Theremaining conductor cores arethen identifiedby reference to their positions relatively to theconductor core which incorporates the recessed formation.

If it is required to identify by a specific marking more than one of theconductor cores the appropriate number of conductor cores, that is twoor more, are then formed with respective longitudinally extendingrecessed forma tions differing from each other in appearance.

The sides of the groove may be convergent with respect to each other ina direction radially inwardly of the conductor core. The preferredcross-sectional shape .of the groove is V-shaped, the angle between thesides of the groove being large enough to permit filling material to beremoved by scraping, abrasion or similar operations.

From a further aspect, the present invention resides in a method ofmanufacture of the kind specified wherein 3,193,614 Fatented July 6,1965 a recessed formation is formed in one at least of the conductorcores of the cable prior to the operation of drawing the cable.

The recess or each of same then become filled with the powderedinsulating material fed into the sheath, and during the drawing down ofthe cable with consequent reduction in the cross-sectional dimensions ofthe conductor core concerned the dimensions of the recess or each ofsame contract, so that the powdered material in the recess becomescompacted and is retained therein.

Where the recessed formation is in the form of a continuous groove thismay be formed by subjecting ungrooved rod or wire stock to an operationwhich dis places the metal of the stock to change the cross-sectionalshape and form the groove (as opposed to removing metal from the stock).One way in which this may be carried out is by subjecting the rod orwire stock to a drawing operation through a die shaped to conform to thegrooved cross-sectional shape required. Alternatively, the rod or wirestock may be subjected to a rolling operation, the roller having arecess-forming part shaped in cross-section to conform to thecrosssectional shape of the groove formed thereby.

The invention is illustrated in the accompanying drawings wherein:

FEGURE 1 is a View in cross-section of a conductor core of a cable ofthe kind specified, preparatory to insertion in the sheath of the cableand after a groove has been formed in this conductor core;

FIGURES 2 and 3 are respectively a longitudinally diametralcross-section and an end elevation of a die for forming the groove shownin FIGURE 1;

FIGURE 4 is a view in side elevation and partly in cross-section of adraw bench apparatus for subjecting thefilled cable to a drawingoperation;

FIGURE 5 is a view in side elevation and partly in cross-section of anapparatus for filling the cable and compacting the insulating material;

FIGURE 6 is an enlarged fragmentary view on the line 66 of FIGURE 5;

FIGURE 7 is an enlarged cross-sectional view of the cable incorporatingthree conductor cores after the drawing operation;

FIGURE 8 is a view in side elevation and partly in cross-section of analternative form of apparatus for drawing the cable;

FIGURE 9 is a view in side elevation and in vertical cross-sectionthrough the axis of a conductor core, and illustrating an alternativeapparatus and method of producing a recessed formation in a conductorcore;

FIGURE 10-isa View in end elevation of the parts shown in FIGURE 9; I

FIGURE 11 is a fragmentary view illustrating an end portion cable withprotruding conductor cores incorporating respective recessed formationspresenting different visual appearances; and

FEGURE 12 is a view similar to FIGURE 1 illustrating a modificationwherein the groove is filled with another material, preparatory toinsertion of the conductor core in the sheath of the cable.

Referring firstly to FIGURE 1 of the drawings wherein is shown incross-section a piece of rod or wire stock =19 of a suitableelectrically conductive material, such as copper, the rod or wire stockmay have any suitable crosssectional shape initially, for example,circular as shown, and according to the size of the cable required to bemanufactured may have an initial diameter ranging typically from about aquarter of an inch to about two inches.

The rod or wire stock is subjected to an operation to produce a recessedformation extending longitudinally of the stock. Such recessed formationmay be a continuous groove 11. The cross-sectional area of the groove11, rela- & tively to that of the rod or Wire stock as a whole, is notcritical but should be such that it does not materially reduce thecurrent carrying capacity of the conductor core after manufacture of thecable has been completed, whilst presenting a sufiiciently broad mouthto be readily visible for the purposes of identification of theconductor core.

In practice I found that a V-section groove, wherein the included anglebetween the side faces is approximately 100 and wherein the depth of thegroove measured radially between its inner extremity and the mouth ofthe groove (as defined by a continuation of the outer boundary of therod or wire stock in cross-section) of the order of one tenth of thediameter of the rod or wire stock, is satisfact-ory.

One of the reasons for preferring a relatively wide angle for the groove11 is that powdered insulating material of the cable, which normallyfills this groove and assists in identification of the conductor core byvirtue of its contrasting visual appearance in relation to that affordedby the surface of the remaining part of the conductor core, can readilybe removed by scraping with a knife or sharp pointed tool or by abrasionwith a file or emery paper, and if need be a portion of the conductorcore, which incorporates the groove, can thereafter be flattened with afile or similar tool so as to avoid any recessed or re-entranceformation. This may be important in certain cases where, havingidentified the conductor core, it is desired to fit a sealed terminationto the cable which will prevent the ingress of liquid or moisture intothe interior of the cable and thereby will maintain the insulationresistance afforded by the filling of the cable at a satisfactorily highvalue.

The groove 11 may be formed by drawing the rod or wire stock through adie of the form illustrated in FIG- URES 2 and 3 wherein it will beobserved that the body 12 of the die affords a die opening 13 includingconvergent sections 14 and15 and a substantially parallel sided portion16. Within the two latter portions 15 and 16 is'provided an inwardlyprojecting nib 17 which is shaped in cross-section to produce the groove11.

Having formed the groove in the rod or wire stock a length of the rod orwire stock, together with an appropriate number of other conductor coresformed of similar rod or Wire stock, is assembled within a tubularsheath and the sheath is then filled with powdered insulating material,such as magnesium oxide, which is compacted.

These operations may be performed by an apparatus as illustratedgenerally in FIGURE 5, wherein the sheath tube 18 is accommodated mainlyin a bore 19 in the floor 20 of the premises in which the apparatus isinstalled.

An upwardly projecting supporting structure or post 21 carries areciprocating ram 22, guided intermediate its ends by a guide member 23,and supported and reciprocated by means of a carriage 24 which is movedupwardly along the post 21 in accordance with the level of the powderedcontent in the sheath tube and which has a driving unit 25 forreciprocating the ram.

Powder is delivered into the sheath tube 18 from a hopper 26 and passesdown an interspace 27 between the outer face of the ram and the innerface of the sheath tube 18. The ram 22 is of hollow form to accommodatethe rods or wires forming the conductor cores and is maintained incoaxial relation with the sheath tube by guide blocks or feathers 28.

After filling of the sheath tube and compaction of the powderedinsulating material therein, the sheath tube, together with the rods orwires and the powdered insulating material, is subjected to a drawingoperation to draw it down to the required size.

An apparatus for performing this operation is illustrated in FIGURE 4wherein 29 designates a suitable drawing die through which the filledsheath tube is drawn by means of a carriage 30 including a means forgripping the leading end of the sheath tube 18 and conductor, and acoupling member 31 for releasable engagement with a draw chain 30 guidedover sprockets, one of which is indi- =2 catcd at 32, driven in anysuitable manner to advance the carriage 30 from left to right as seen inFIGURE 4.

An alternative form of apparatus for performing the drawing operation isillustrated in FIGURE 8 wherein the sheath tube 118 and a suitable die129 are shown, the leading end portion of the sheath tube being held bya gripping dog member 13h provided on a Winding drum 131 rotated in thedirection of the arrow 132 by any suitable drive means.

FIGURE 7 illustrates in cross-section the form of the cable produced asa result of the drawing operation.

Three conductor cores are illustrated, namely 33 (formed from the rodand wire stock 19 shown in FIG- URE 1), 34 and 35, of which the last twomentioned are not formed with any recessed formation. All theseconductor cores are of single-strand or homogeneous form incross-section.

The powdered insulating material 37, which mechanically separates andelectrically insulates the con-ductor cores 33 to 35 from each other andfrom the sheath tube, fills the groove 36 in the conductor core 33 (suchgroove being in effect a reduction of the groove 11 in FIGURE 1). Thepowdered insulating material is normally retained in the groove 36 whenthe conductor cores are exposed by cutting away the sheath tube 18 andremoving the insulating material, and since the latter is normally whitein colour the marking produced by this filling of the groove 36 on theconductor core 33 is clearly apparent.

However, the filling of insulating material can be removed from thegroove 36, as previously referred to, if desired.

The conductor cores do not become twisted or transposed within thesheath tube 18, so that ordinarily it is necessary only to identify oneconductor core at each end of the cable where the conductor cores arenormally exposed and then the other unrecessed conductors 34 and 35 bytheir positions relatively to the other recessed conductor core 33.

However, in cases where it is desired to provide for specificidentification of each or more than one of the con ductor cores, thesemay be formed with respectively different recessed formations, asillustrated in FIGURE 11.

As seen therein, the conductor cores 233, 234 and 235 protrude from afilled sheath tube 218.

The conductor core 233 has a groove 236 which may be of V-shape similarto the groove 36 shown in FIGURE 7, whereas the conductor cores 234 and235 have dis continuous recessed formations, in the former thisconsisting of a series of elongated recesses 237 and in the latter casea series of conical recesses 238, in both cases these recessescontaining filling of the powdered insulating material.

The manner of forming recesses such as 237 and 238 is illustrated inFIGURES 9 and 10.

The rod or wire stock 310, from which the conductor cores are formed,may thus be passed between a pair of rolls 339 and 349, each formed witha peripheral groove of part-circular shape in cross-section to embraceand enclose the stock, as seen in FIGURE 10.

One of these rolls, for example 349, is formed in the base of thisgroove with a plurality of radial projections 350 which may be ofconical form (for forming recesses such as 238), or possibly ofelongated form were it desired to form recesses such as 237. The rolls339 and 349, or at least one of them, preferably in this case thatincorporating the projections 350, would be connected in any suitablemanner to a drive motor, The apex angle of the conical recesses formedmay be equal to that of the V-section groove, namely or thereabouts.

FIGURE 12 illustrates a further modification of rod or wire stock 410,wherein the recessed formation or groove 411 contains a filling 412 of amaterial other than the insulating material used to fill the sheathtube. This modification may be adopted in either of two cases. Firstlywhere it is desired that the conductor core as a whole shall bemaintained to strictly circular shape in cross-section, thereby avoidingany difiiculty in achieving sealing at a cable termination, and secondlywhere it is desired that the current capacity of the conductor coreshall not be diminished to any extent at all.

In the first case the filling material 412 may be either an insulatingmaterial or a metal, the surface of which presents a contrasting visualappearance with respect to that afforded by the remainder of theconductor cores.

In the second case the filling would be of an electrically conductivemetal. Where the conductor core 410 is made of copper a suitable metalfor this purpose would be tin or a tin lead alloy, or possibly aluminum.

In any case where this filling of the recessed formation is performedprior to the insertion of the rod or wire stock into the sheath tube andprior to the drawing down of the latter, the filler material should beselected so as to be capable of undergoing the drawing operation withoutbreaking up into fragments and coming out of the recessed formation.

What I claim then is:

1. An electrical cable comprising a sheath, a plurality of conductorcores disposed in said sheath, at least one of said cores beinginitially provided with a wide-angled recess disposed in axial alignmenttherewith, and loose insulation material, said material being firmlypacked within said sheath to space said conductor cores from each otherand from said sheath, and said material being firmly packed into saidrecess to visually distinguish the filled recess cross-section of saidone core from the integral cross-sections of said remaining cores.

2. An electrical cable having readily identifiable conductor corestherein, said cable comprising a tubular metal sheath, a plurality ofconductor cores extending therethrough, insulating material disposed insaid sheath spacing and electrically insulating said cores from eachother and from said sheath, at least one of said cores having alongitudinally extending recessed formation in its surface, fillingmaterial disposed in said formation, said filling material having acontrasting visual appearance to that of said surface to identify saidone core from the remaining cores in said sheath, said formation havinga readily visible mouth defined by edges spaced apart at said surface ina direction circumferentially thereof.

3. An electrical cable having readily identifiable conductor corestherein, said cable comprising a tubular metal sheath, a plurality ofconductor cores extending therethrough, insulating material disposed insaid sheath spacing and electrically insulating said cores from eachother and from said sheath, said insulation material presenting adifferent visual appearance from that of said cores, at least one ofsaid cores having a continuous longitudinally extending groove in itsouter surface, said groove being filled with said insulating material todistinguish it from the remainder of said cores.

4. An electrical cable according to claim 2 wherein at least one of saidcores is provided with a longitudinally extending series of spacedrecesses in said surface, each of said recesses being filled with saidinsulating material.

5. An electrical cable according to claim 2, wherein said conductors aresingle strand cores of substantially circular cross-section, saidformation having a readily visible mouth defined by closelycircumferentially spaced edges, said formation extending inwardly fromsaid surface through a short distance relative to the cross-sectionradius of said core.

6. A method of making an electric cable having readily identifiablecores therein, said method comprising the steps of assembling lengths ofelongated metal stock, forming conductor cores from said stock, forminga longitudinally extending recess in at least one of said cores,inserting a plurality of said cores including said recessed core througha sheath-forming tube, introducing powdered material through one end ofsaid tube, packing said material within said tube to fill said recessand electrically insulate said cores from each other and said tube, andthen reducing said tube to a predetermined crosssectional dimension.

7. The method according to claim 6, including the steps of drawing saidone core through a die having a crosssectional shape complementary tosaid stock and forming a continuous groove therein.

8. The method according to claim 6, including the steps of formingsubstantially circular cores from said stock and then rolling said onecore between rollers which in combination define an aperture of across-sectional shape complementary to that of said core while formingsaid recess with side faces which are convergent with respect to eachother in a direction radially inwardly of said one core at an angle in arange exceeding a value of approximately degrees.

References Cited by the Examiner UNITED STATES PATENTS 689,615 12/01Heyl-Dia 174-133 X 2,036,034 3/36 Fulmer et al. 29547 X 2,973,706 3/61Kingsley.

3,136,054 6/64 Palmer et al. 29-547 FOREIGN PATENTS 573,607 4/59 Canada.

OTHER REFERENCES A.P.C. application of Beckett, Serial No. 218,848,published June 8, 1943.

JOHN F. BURNS, Primary Examiner.

JOHN P. WILDMAN, E. JAMES SAX, Examiners.

1. AN ELECTRICAL CABLE COMPRISING A SHEATH, A PLURALITY OF CONDUCTORCORES DISPOSED IN SAID SHEATH, AT LEAST ONE OF SAID CORES BEINGINITIALLY PROVIDED WITH A WIDE-ANGLED RECESS DISPOSED IN AXIAL ALIGNMENTTHEREWITH, AND LOOSE INSULATION MATERIAL, SAID MATERIAL BEING FIRMLYPACKED WITHIN SAID SHEATH TO SPACE SAID CONDUCTOR CORES FROM EACH OTHERAND FROM SAID SHEATH, AND SAID MATERIAL BEING FIRMLY PACKED INTO SAIDRECESS TO VISUALLY DISTINGUISH THE FILLED RECESS CROSS-SECTION OF SAIDONE CORE FROM THE INTEGRAL CROSS-SECTIONS OF SAID REMAINING CORES.